1. Field of the Invention
The present invention generally relates to transportation of a substrate using an end effector which mechanically clamps the periphery of the substrate, in particular, to a method for reducing particle generation at a bevel portion of the substrate during the transportation.
2. Description of the Related Art
In semiconductor or liquid crystal display (LCD) manufacturing, micro particle generation which occurs at substrate edges is a serious concern. Micro particles are generated when the edge of a substrate such as a Si wafer is scratched by a clamping device of a substrate transfer robot to mechanically clamp the edge of the substrate. Also, when a film deposited on a substrate edge surface is scratched by a clamp and partially peeled, micro particles are generated. This problem most likely occurs when the film having tensile mechanical stress (“tensile film”) is deposited on the substrate surface, which film easily peels off from the substrate surface. After these particles generated at the edge of the substrate are detached from the substrate surface, they move over the surface and adhere to the substrate surface, causing electrical damage to a highly integrated circuit and leading to serious yield reduction.
In order to prevent particle generation by mechanical clamping at the edge of a substrate, a vacuum chuck for a substrate backside surface is well-known means. However, this device cannot be adapted to transfer a substrate under a vacuum environment. In addition, when a substrate is transported using a vacuum chuck, particles are generated in an area where the vacuum chuck is attached, giving rise to a concern on accuracy of the subsequent processes such as a lithography process since particles on the substrate backside may shift the focal point by a micron order when patterning is performed using an exposure device. FIG. 7 shows particles on the backside of a substrate after the substrate was aligned using a notch aligner of vacuum chuck type wherein a vacuum chuck was attached at the center of the substrate (the diameter of the suction area was about 40 mm, and suction pressure was 60 to 80 kPa less than the standard atmospheric pressure). For these reasons, the vacuum chuck method does not meet the requirements for highly integrated modern semiconductor manufacturing. Other than the vacuum chuck, simply slowing down the substrate transfer speed without using any chuck devices is an often used option. This measure, however, increases the overall substrate transfer time and leads to a serious problem of low productivity.
Any discussion of problems and solutions in relation to the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.